Battery operated autonomous scale removal system for wells

ABSTRACT

An autonomously operated well intervention tool system includes a lubricator sealingly affixable to an upper end of a well. The lubricator has a latch at an upper end thereof. A well intervention tool system is releasably matable with the latch. The well intervention tool system comprises a wellbore intervention device at a longitudinal end thereof. The lubricator has at least one isolation valve to close fluid communication between the well and the lubricator.

BACKGROUND

This disclosure relates generally to the field of a non-tetheredautonomous well intervention tool system for removing scale and similarfrom a wellbore. The wellbore can be subsea, on an offshore platform oron land. More specifically, the present disclosure relates to a batteryoperated electrical tool for dissolving mineral build-up in a wellbore,where the tool is stored, deployed from and received in a lubricator andcharging system mounted on top of a wellhead (Christmas tree). Thewellbore intervention tool system may also perform other wellboreoperations, e.g., production logging, setting and retrieval of plugs,and other intervention operations known in the art. The system mayoperate without the presence of a human operator at the well site,either remotely operated or autonomously at pre-determined times.

Buildup of scale and paraffin is a frequent problem in producinghydrocarbon wells, where such build up causes drop or total halt ofproduction as well as malfunction of wellbore completion components, forexample, downhole safety valves. To remove scale and paraffin deposits,wireline is rigged up on top of the wellbore, followed by anintervention where electrical or mechanical impact based tools are runinto the wellbore to hammer loose the scale or cut the paraffin builtup. This is a slow process due to the nature of the tools being used,but not least due to the time required to rig up and down theintervention valves, lubricator and so on. In addition, well productionis lost due to the required well “shut in” (stopping of fluidproduction) during rigging operation. The process may also be expensive,where the cost of performing an intervention in a subsea well can amountto tens of millions of United States dollars, plus a significant lostincome for the duration of the intervention.

Due to the foregoing considerations, failures of wellbore components,for example, downhole safety valves, also take place as a result ofintentionally infrequent scale removal, causing the production tubing,etc., to become partially or completely non-functional.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1. illustrates scale in a tube, where it can be understood thatthis will reduce or totally prevent flow through a tube as well as causewellbore components to malfunction.

FIG. 2 illustrates a wellhead with an attached wellhead (“christmastree”) and a lubricator/valve system installed on top of the christmastree. Within the lubricator, a wellbore intervention tool system ismounted. Scale build up is indicated within a conduit called productiontubing.

FIG. 2A shows an enlarged view of an example intervention tool system

FIG. 3 illustrates that valves in the lower end of the lubricator systemhave been opened, followed by a wellbore intervention tool moving intothe wellbore.

FIG. 4 illustrates that one or both valves in the lower section of thelubricator system have been closed, so that the well can be flowed at alow rate with the intervention tool being downhole. Scale removal may bestarted.

FIG. 5 illustrates that the intervention tool is transported up-hole,either by producing the well or by a built in propulsion drive.

FIG. 6 illustrates that the intervention tool has latched into the topsection of the lubricator/valve system, with both valves closed and wellbrought back to normal production.

DETAILED DESCRIPTION

Therefore the present disclosure sets forth a possible solution toremoving scale or paraffin in a well where the scale or paraffin removalis performed more frequently than may be performed using conventionalwireline conveyed tools. Increased frequency of scale or paraffindeposits may prevent excessive buildup of such scale or paraffindeposits. Scale or paraffin removal at more frequent intervals may beperformed by a system mounted on top of the wellhead, where alubricator, isolated from the wellhead by valves built into the lowersection of the intervention system, contains a scale or paraffin removaltool that can be deployed into the wellbore when required.

The wellbore tool intervention system may include a scale or paraffinremoval tool with required ancillary instrumentation attached, such as,for example, a battery package, a wet-mating electrical coupler, apropulsion system, etc. The wellbore tool intervention system may bedeployed into the wellbore from a storage place within the lubricatorand may be returned to the lubricator by causing fluid to flow from theformations external to the well thence into the well. In someembodiments, the wellbore intervention tool system may contain apropulsion system built in that returns the wellbore tool system to thelubricator when required.

Electrical, hydraulic or pneumatic operated impact (e.g. hammer, socalled “broach” and similar) based scale removal tools can be coupled tothe wellbore intervention tool system. A wellbore intervention toolsystem according to the present disclosure allows more frequent wellborescale or paraffin removal operations than would be ordinarily performedusing interventions from a vessel, workover rig or a drilling rig. Morefrequent deposit removal may result in the scale or paraffin depositsbeing of less extent than would occur with less frequent intervention;such more frequent deposit removal ensures improved production ofhydrocarbons from the well.

To perform a wellbore intervention, pressure equalizing between thewellbore and the lubricator may be performed, followed by opening ofvalves between the lubricator and the wellhead. This will enable thewellbore intervention tool system to drop, or drive down, into thewellbore where it reaches a restriction caused by scale or paraffin.Then the removal of such restriction will be commenced, until therestriction has been removed or until an internal power source (e.g.,batteries) is exhausted. When the foregoing takes place, the wellboreintervention tool system may be transported up to the lubricator againby a built in “swab cup” that uses fluid flow from the wellbore to liftthe wellbore intervention tool system. When reaching the wellhead, thewellbore intervention tool system will be further pushed up into thelubricator and latch onto a holding device and/or an electrical couplerenabling battery recharging.

After the wellbore intervention tool system has been returned to thelubricator, the valves between the lubricator and the wellhead can beclosed and pressure tested, so that the well can commence fluidproduction again.

When scale or paraffin removal is required again, the above sequence maybe repeated.

For those skilled in the art of wellbore interventions, it will beunderstood that the method described herein may also be used for othertype interventions, e.g., memory type production logging, and otherintervention operations.

FIG. 1. illustrates scale 14 in a tube 12. The tube 12 may be, forexample, a wellbore production tubing or “velocity string.” It will beappreciated that the scale 14 will reduce or totally prevent flowthrough the tube 14. The scale 14 may also cause wellbore components tomalfunction. Such scale needs to be removed, where various methods canbe used, as for example mechanically breaking the scale, pulsedelectrical energy pulverizing the scale, release of scale-dissolvingchemicals, or abrasive means such as milling.

FIG. 2 illustrates a wellhead 20, for example a sea bottom wellhead withan attached christmas tree (e.g., valves 30 and 32). A lubricator system22 may be affixed to the upper end of the wellhead. The lubricatorsystem 22 may include isolation valves 22A such as gate valves toselectively pressure isolate the lubricator system 22 from the wellhead20. The isolation valves 22A may be operated by respective actuators22B. The actuators 22B may be electrically, pneumatically orhydraulically operated, for example. The lubricator system 22 mayinclude pressure equalization valves 28 that connect the interior of thelubricator system to below each of the isolation valves 22A. Thepressure equalization valves 28 may also be actuated electrically,hydraulically or pneumatically. The isolation valves 22A and thepressure equalization valves 28 may be operated by a controller 29. Thecontroller 29 may be operated using, for example, telemetry from thewater surface or electrical connection using a remotely operated vehicle(ROV). The lubricator system 22 may also include a pressure relief valve24 to enable release of pressure from the interior of the lubricatorsystem after the well intervention tool system 10 is retrieved into thelubricator system 22. The pressure relief valve 24 may also beelectrically, hydraulically or pneumatically operated and may becontrolled by the controller 29.

The upper end of the lubricator system 22 may include a sealing cover22D that is retained in place on the upper end of the lubricator system22 and is pressure sealed. The sealing cover 22D may include anautomatically operable latch 22E to retain the wellbore interventiontool system 10 when it is retrieved into the lubricator system 22. Thelatch 22E may include electrical connections (not shown separately) forproviding electrical power to the wellbore intervention tool system 10,e.g., to recharge batteries therein (see FIG. 2A).

The sealing cover 22D may have a profile for a retrieval and runningtool, a receptacle 22F for an electrical cable from an external powersource as well as various sensors for monitoring pressure, etc. It mayalso contain a telemetry system for transmitting and receiving commandsand data from a surface vessel or the like. The sealing cap 22D may alsobe removed, so that a wellbore intervention pressure control system(with riser, etc.) can be landed on top of the lubricator system 22,followed by the possibility of deploying and setting plugs and otherequipment in the wellbore. Setting a plug within a tubing hanger orfurther down into the wellbore tubing 14 may enable a safe removal ofthe complete lubricator system 22 if such is required.

The isolation valves 22A valve system on the lower end of the lubricatorsystem 22 may be used for pressure testing of the lubricator system 22and enable the well to operate normally without subjecting thelubricator system 22 to wellbore production fluids and pressure when thewellbore intervention tool system 10 is not in use.

FIG. 2A shows the wellbore intervention tool system 10 in more detail.The wellbore intervention tool system 10, hereinafter “tool” forconvenience, may include a self-contained power supply 10E such asbatteries within a pressure sealed housing 11. A control and powermodule 10F disposed in the housing 11 may be used to operate a wellboreintervention device 10A. In the present embodiment, the wellboreintervention device may be a scale removal device disposed proximate thebottom of the housing 11. The scale removal device may be any type knownin the art, including a chemical storage and release mechanism,motor-rotated blades or abrasive mills, electric shock (sparker)discharge devices, acoustic devices, heater(s) to remove paraffindeposits, or any other such device for removal of deposits in the tubing(12 in FIG. 1). The tool 10 may include combinations of any or all ofthe foregoing as well. The tool 10 may include a propulsion device 10G,such as a fluid operated jet or a propeller to cause the tool 10 to movewithin the tube 14 during operations if gravity is insufficient to movethe tool 10 downwardly to the depth of any obstruction, and to returnthe tool 10 to the lubricator system (22 in FIG. 2) if fluid flow fromthe well is insufficient to lift the tool 10. The housing 11 may includeannular seals 10D such as swab cups to enable free movement of the tool10 downwardly, but may seal to engage the interior of the tubing (14 inFIG. 1) to enable fluid flow into the well to lift the tool into thelubricator system (22 in FIG. 2). The upper end of the housing 11 mayinclude a mating latch 10B to engage the latch (22E in FIG. 2) in thelubricator system sealing cover (22D in FIG. 2). The housing 11 mayinclude centralizers 10C to enable relatively free movement of the tool10 in the tubing (14 in FIG. 2) and to keep the tool 10 centered in thetubing for proper operation of the scale removal device.

Scale or paraffin build up may be indicated within the production tubing(14 in FIG. 2), for example, by a decrease in fluid production from thewell. Thus it may be necessary to deploy the tool 10. The tool 10 may beinstalled into the lubricator system (22 in FIG. 2) prior to installingthe lubricator system (22 in FIG. 2) onto the wellhead (20 in FIG. 2) orthe tool 10 may be installed into the lubricator system (22 in FIG. 2)by unlatching and removing the sealing cover (22D in FIG. 2). Retrievalof the tool 10 may be performed by unlatching and retrieving the entirelubricator system with the tool 10 inside the lubricator system, or byunlatching the sealing cover (22D in FIG. 2) and retrieving the tool 10.It is also possible to perform tool replacement using an ROV in marineoperations where the wellhead is on the water bottom.

In other embodiments, the wellbore intervention device 10A may be anyother type of wellbore tool, including, without limitation, a productionlogging instrument, a plug or packer setting tool or a video camera.

FIG. 2 shows the tool 10 engaged with the latch 22E and the isolationvalves 22A and pressure equalization valves 28 closed so that the wellcan operate normally. When it is determined that deployment of the toolis necessary, FIG. 3 illustrates that the pressure equalization valves28 may be opened to equalize pressure in the well with the pressure inthe lubricator system 22. The isolation valves 22A may then be openedand the latch 22E may be released to enable the tool 10 to movedownwardly through the well tubing 14. Movement of the tool 10 into thewellbore may be by gravity or by a propulsion device (10G in FIG. 2A) inthe tool 10. It is also here illustrated that the tool performs scale orparaffin removal.

FIG. 4 illustrates that one or both of the isolation valves28 has beenclosed, so that well can be flowed at low rate with the tool 10 being inthe wellbore. Scale or other deposit removal may then be started byoperating the deposit removal device 10A. When the tool 10 reaches thearea of restriction caused by scale or paraffin, the tool 10 performsthe removal of this restriction as explained above. As the deposits areremoved and the flow restriction is alleviated, the tool 10 will by movefurther down into the wellbore by gravity (or by use of the propulsiondevice 10G in FIG. 2A, e.g., for highly inclined or horizontal wells)The tool 10 control and power module (10F in FIG. 2A) may include aninternal mechanism that detects length of free fall, e.g., integratingaccelerometers or an integrating velocity meter and/or area with nounwanted restriction. The power and control module may be programmed toenable the tool 10 to stop itself, e.g., by energizing its swab cups(10D in FIG. 2A), a mechanical breaking mechanism or the propulsiondevice (10G in FIG. 2A.

A device preventing the tool 10 from going further into the wellborethan a selected depth may also be installed in the wellbore, forexample, a narrow internal diameter packer or similar restriction. Sucha device can be set up to trigger the power and control module (10F inFIG. 2A) to cause the tool 10 to return the lubricator/system 22. Anexample of such device may be a contact switch, shown at 13 in FIG. 2Awhich would not be triggered by scale or other deposits, but would betriggered by contact with a packer or similar internal diameterrestriction.

FIG. 5 illustrates that the tool 10 is transported up-hole, either byproducing the well at low flow rate or by the propulsion device (10G inFIG. 2A). The isolation valves 28 are opened to enable the tool 10 toenter the lubricator system 22.

FIG. 6 illustrates that the tool 10 has latched into the lubricatorsystem 22 on the latch 22E in the sealing cover 22D. At such time theisolation valves 28 may be closed and the well brought back to normalproduction. The tool 10 is now coupled to the electrical coupler (partof latch 22E) in the sealing cover 22D so that the batteries (10E inFIG. 2A) can be charged. In some embodiments it may be possible toretrieve logged data and transmit new commands to the tool 10 throughthe electrical connector 22F.

After the isolation valves 28 are closed, pressure inside the lubricatorsystem 22 may be released using the pressure relief valve 24. Such maybe performed prior to any required removal of the sealing cap 22D or thelubricator system 22 from the wellhead 20.

While the invention has been described with respect to a limited numberof embodiments, those skilled in the art, having benefit of thisdisclosure, will appreciate that other embodiments can be devised whichdo not depart from the scope of the invention as disclosed herein.Accordingly, the scope of the invention should be limited only by theattached claims.

What is claimed is:
 1. An autonomously operated well intervention toolsystem, comprising: a lubricator sealingly affixable to an upper end ofa well, the lubricator comprising a latch at an upper end thereof; awell intervention tool system releasably matable with the latch, thewell intervention tool system comprising a wellbore intervention deviceat a longitudinal end thereof; and wherein the lubricator comprises atleast one isolation valve to close fluid communication between the welland the lubricator.
 2. The system of claim 1 wherein the latch comprisesan electrical connector to enable supply of electrical power to the wellintervention tool system.
 3. The system of claim 1 wherein an electricalconnector is located anywhere within the lubricator system.
 4. Thesystem of claim 1 wherein the wellbore intervention device comprises ascale removal device.
 5. The system of claim 1 wherein the wellboreintervention device comprises at least one of a production logginginstrument and a plug or packer setting tool.
 6. The system of claim 1wherein the well intervention tool system comprises at least one swabcup on an exterior surface thereof to enable lifting the wellintervention tool system by upward movement of fluid in the well.
 7. Thesystem of claim 1 wherein the well intervention tool system comprises apowered propulsion unit to enable movement of the well intervention toolsystem along an interior of the well.
 8. The system of claim 1 whereinthe lubricator comprises at least one equalization valve in a fluidcommunication line extending between the well and the lubricator.
 9. Thesystem of claim 1 wherein the lubricator comprises at least one pressurerelief valve configured to selectively vent pressure inside thelubricator.
 10. The system of claim 1 wherein the scale removal devicecomprises at least one of a chemical storage and release mechanism,motor-rotated blades, motor-rotated abrasive mills, an electric shockdischarge device, an acoustic device and a heater.
 11. The system ofclaim 1 wherein the well intervention tool system comprises means forautomatically stopping the well intervention tool system at a selectedposition in the well.
 12. A method for performing interventionoperations in a well, comprising: latching a well intervention toolsystem in a lubricator, the lubricator comprising at least one isolationvalve at a well connection end thereof, the lubricator comprising atleast one pressure equalization valve, the lubricator comprising atleast one pressure relief valve; closing the at least one isolationvalve; affixing the lubricator to an upper end of a well; opening the atleast one pressure equalization valve to impart pressure in the well toan interior of the lubricator; opening the at least one isolation valve;releasing the well intervention tool system to move into the well toselected depth therein; operating a wellbore intervention device on thewell intervention tool system; and returning the well intervention toolsystem to the lubricator.
 13. The method of claim 12 wherein thereturning the well intervention tool system to the lubricator compriseslifting the well intervention tool system using flow of fluid in thewell.
 14. The method of claim 12 wherein the returning the wellintervention tool system to the lubricator comprises operating apropulsion device in the well intervention tool system.
 15. The methodof claim 12 further comprising closing the at least one isolation valve,opening a pressure relief valve to vent pressure from within thelubricator and removing the lubricator from the well.
 16. The method ofclaim 12 further comprising closing the at least one isolation valve,opening a pressure relief valve to vent pressure from within thelubricator, removing a sealing cap from an upper end of the lubricatorand retrieving the well intervention tool system from within thelubricator.
 17. The method of claim 12 further comprising attaching anelectrical cable to a connector forming part of a latch used to retainthe well intervention tool system in the lubricator and applyingelectrical power to the electrical cable to recharge at least onebattery in the well intervention tool system.
 18. The method of claim 12wherein the wellbore intervention device comprises a scale removaldevice.
 19. The method of claim 12 wherein the wellbore interventiondevice comprises at least one of a production logging instrument and apacker or plug setting tool.